A Wide-Load-Range Mixed-Mode LDO Regulator with Single-Transistor-Assisted Buffer

Abstract

A wide-load-range low-dropout (LDO) regulator with single-transistor-assisted buffer and analog-digital mixed-mode control is presented in this paper. The single-transistor-assisted PMOS-input unity-gain-buffer can extend the gate voltage range of the analog power transistor and guarantee that the proposed LDO regulator can work well even at very light load current. To extend the loading capability for large load current, a mixed-mode control is used to detect heavy load and turn on or off the digital power transistor which provides large current to the load with better area efficiency. With the digital assistance, the proposed LDO regulator has better load regulation and loading capability at heavy load as well. A proof-of-concept design of the proposed LDO regulator has been implemented and fabricated in a standard $0.18-\mu \mathrm {m}$ CMOS process. It occupies an active area of only $0.01 \mathrm {m}\mathrm {m}^{2}$. With the load current step from 0 mA to 150 mA, the proposed LDO regulator with digital assistance achieves a droop voltage reduction of more than 50% compared to the design without the digital assistance. A load regulation of 0.21 mV/mA is achieved by the proposed design with the help of the digital assistance and single-transistor-assisted buffer.